Obesity refers to excess of body fat resulting in a Body Mass Index (BMI which is a ratio of weight to height) of 30 or more.
Other definition:
Obesity is defined as an excessive accumulation of body fat, believed to contribute to a variety of health disorders, including cardiovascular disease. Moreover, Obesity is the excess of body fat resulting in a body mass index (a ratio of weight to height) of 30 or more; having a body mass index (BMI) of 30 or greater.